Biaxial strain-mediated magnetic phase transition and anisotropy engineering in the MoSBr monolayer: a first-principles approach for room-temperature spintronics.

Precise and nonvolatile control of magnetic order in two-dimensional (2D) ferromagnetic semiconductors is essential for advancing low-power spintronics. Strain engineering provides an efficient approach toward this goal. Here, first-principles calculations are employed to investigate the influence of biaxial strain on the magnetic properties of the MoSBr monolayer. The unstrained MoSBr monolayer exhibits in-plane magnetic anisotropy with a Curie temperature (TC) of 190 K. Under biaxial tensile strain, the magnetic anisotropy energy increases dramatically, reaching 1.41 meV per unit cell at 12% strain. Furthermore, a strain-driven spin-reorientation transition (from in-plane to out-of-plane) occurs at 4.65% tensile strain. Remarkably, TC surpasses 300 K at 12% tensile strain, while a modest compressive strain (-1.44%) induces a ferromagnetic-to-antiferromagnetic transition. Structural stability of the monolayer across a wide strain range (-8% to +12%) is confirmed through phonon spectrum analysis and ab initio molecular dynamics simulations. Quantitative relationships are established between strain and magnetic properties. Specifically, strain-mediated crystal-field distortion selectively alters d-orbital occupancies and the hierarchy of spin-orbit coupling matrix elements, thereby modulating magnetic exchange interactions. These results suggest that MoSBr is a highly promising, strain-tunable 2D magnet, providing a design principle for engineering the functionality of 4d-based magnetic materials for spintronic applications.